You absolutely can turn it off - it's called quenching the magnet, and the tech absolutely should have been trained to do that in an emergency. There was no way in hell they were physically pulling him off. It's obviously that they did eventually, but the article doesn't say how long it took 🤷‍♂️ to be fair, I'd bet that basically all of the damage was done up-front, regardless - MRI magnets are so much stronger than most people realize.